Microwave Engineering
EEC 222
Lecture (4)
Microwave passive elements &
design of microwave matching
networks
Prepared by :
Dr. Amaal Ashraf
4.1 Introduction
• Active and passive microwave devices and components are the essential
building blocks of microwave circuits and systems that operate in the
frequency range from 300MHz to 300GHz (corresponding to wavelengths
of 1m to 1mm in free space).
• Microwave circuits are a combination of passive and active components.
Without passive components (e.g., filters, matching circuits, circulators,
isolators resistors, etc.), active components ( e.g., transistors, tubes) cannot
be operated.
• Microwave passive components may be composed of lumped elements
(inductors, capacitors, and resistors) or distributed elements (transmission
line sections) or both.
Microwave Engineering EEC 222 2
4.2 Impedance Transformers and Matching Networks
• The purpose of an impedance transformer is to transform a given impedance
to a specific value. An impedance matching network may consist of more
than one impedance transformer.
• Its main goal is to match a given impedance to a prescribed value over a
frequency range of interest to ensure maximum power transfer from a source
to a load.
• Typical applications include returning loss optimization between an antenna
and low- noise amplifier.
• Impedance transformers and matching networks are perhaps the most
important and most widely used passive microwave circuit component.
Microwave Engineering EEC 222 3
4.2 Impedance Transformers and Matching Networks
• The basic idea of impedance matching is illustrated in Figure 4.1, which
shows an impedance matching network placed between a load impedance
and a transmission line. The matching network is ideally lossless, to avoid
unnecessary loss of power.
• This procedure is sometimes referred to as tuning.
Figure 4.1 Schematic Description of a Two Port Passive Impedance
Microwave Engineering EEC 222 4
Impedance matching or tuning is important for the following reasons:
Maximum power is delivered when the load is matched to the line (assuming
the generator is matched), and power loss in the feed line is minimized.
Impedance matching sensitive receiver components (antenna, low-noise
amplifier, etc.) may improve the signal-to-noise ratio of the system.
Impedance matching in a power distribution network (such as an antenna
array feed network) may reduce amplitude and phase errors.
Microwave Engineering EEC 222 5
4.2.1 Lumped-Element Transformers (L –Networks)
• Transmission-line base impedance transformation is made possible through
distributed effects, which may also be realized by using lumped- element-
based networks in terms of capacitors and inductors.
• Capacitors and inductors connected in L/𝝅- shaped configurations are
widely used as impedance matching networks.
• There are eight possible arrangements of the L C network topology, as
shown in Figure 4.2.
Microwave Engineering EEC 222 6
4.2.1 Lumped-Element Transformers (L –Networks)
Figure 4.2 Generalized Lumped-Element Network Transformers with Various L-C Combinations
Microwave Engineering EEC 222 7
4.2.1 Lumped-Element Transformers (L –Networks)
• Analytic Solution for ZL< Z0
• Rearranging and separating
into real and imaginary parts
gives:
Microwave Engineering EEC 222 8
4.2.1 Lumped-Element Transformers (L –Networks)
• Analytic Solution for ZL > Z0
• Rearranging and separating
into real and imaginary
parts gives:
Microwave Engineering EEC 222 9
Example 1
Microwave Engineering EEC 222 10
Example 1
Microwave Engineering EEC 222 11
Example 1
Microwave Engineering EEC 222 12
Example 1
Microwave Engineering EEC 222 13
Example 1
Microwave Engineering EEC 222 14
Example 1
Microwave Engineering EEC 222 15
Example 2
Microwave Engineering EEC 222 16
Example 2
Microwave Engineering EEC 222 17
Example 2
Microwave Engineering EEC 222 18
Example 2
Microwave Engineering EEC 222 19
Example 2
Microwave Engineering EEC 222 20
